MMGs were prepping belt for splicing PP-P3. MMG picked up 1/4"" die grinder w/buffing wheel, pressed trigger to test prior starting work. The quick connect holding 3"" buffing wheel sheared at the base of the shaft nearly instantly upon rotation, sent buffing wheel/quick connect spinning to the right side of the tool, striking a nearby MMG ~3 ft to top of left-hand knuckle area.